In this experiment, Damasio used Positron Emission Tomography to observe the level of activity in different parts of the brain in association with feelings. The subjects were asked to think of a powerful emotional moment in their lives in as much detail as they can with as much imagery as possible. Damasio looked at the cingulate cortex, the somatosensory cortices of the insula and SII, and the nuclei in the brain stem tegmentum and saw patterns of activation or deactivation that differed among the emotions being re-enacted. For example, for subjects that enacted a sad episode, there was a reduction in activity in prefrontal cortices while for those who enacted a happy episode, there was an increase in activity. This proved that renewing a feeling was associated with changes in the neural mappings of body state. Damasio also observed that changes in skin conductance always came before the subject gave a signal that the feeling was being felt. The body provided an emotional reaction before the subject was even consciously aware of the emotion. This served as further proof that emotional states occur before feelings.